As disclosed in JP 2012-80388 (corresponding to US 2012/0081256 A), a conventional antenna apparatus includes an antenna cover (hereinafter referred to as a case) in which a global positioning system (GPS) antenna, a digital television (DTV) antenna, a radio antenna are arranged. The antenna cover is protruded from an outer surface of a vehicle body.
In an antenna apparatus, a transmission loss in a transmission cable increases with an increase of a frequency of a radio wave utilized for a communication. The frequency of the radio wave is set for an intended application of the antenna apparatus. Specially, in an antenna apparatus used for a vehicle-to-vehicle communication and a road-to-vehicle communication, the radio wave utilized for the communication has a high frequency range of, for example, within a 5.9 gigahertz (GHz) band. Thus, the antenna apparatus has a large transmission loss. In order to reduce the transmission loss in the antenna apparatus, antenna elements may be arranged adjacent to a circuit portion, which configures at least a part of a wireless communication circuit. For example, the antenna elements and the circuit portion may be arranged on the same substrate.
In the antenna apparatus disclosed in JP 2012-80388, when the circuit portion is arranged on the substrate, the circuit portion is arranged in the case together with the substrate. Thus, heat generated by the circuit portion is accumulated in an inside space of the case without being released to an outside of the case. Thus, a performance of the circuit portion may be degraded. Specifically, when the case is arranged on a vehicle roof, the performance may degrade more easily by radiated solar heat. Since the case configures a part of the outer surface of the vehicle body, use of a cooling fun and opening a vent hole are limited by a design limitation.
Further, a thermal stress against a usage environment, a vibration of the vehicle, a stress generated in assembling of the substrate including the circuit portion to the case are applied to a coupling portion between the circuit portion and the antenna elements. Thus, a required lifetime of the coupling portion may be not secured due to the above-described reasons.